If you turn off the slowly changing dimensions for a field, the current dimensional row can be updated with a new value without the addition of a new dimensional row.
You can control slowly changing dimensions for a data source on a field-by-field level by making adjustments to mappings.tcsv for that data source, which is in <PDW install Folder>\star\etl_homes\staretl<id>\res.
A Y or N flag for each field in the mappings file controls whether a change to this field would cause a new row to be added to the dimensional table. Y indicates that a change will cause a new row to be added. N indicates that a new row will not be added if a change is made to this field. For example, if the Activity Description field has a Y flag, then changes made to this field will cause a new row to be added to the dimensional table the next time the STARETL process is run. If the EPS Name field has an N flag, then the STARETL process will not update the dimensional table with a new row. Configuring the Y or N flag for each field can prevent cascading updates to fact tables. For example, if a change is made to the EPS table, that change would cause a new row to be added to the dimension table for all of the activities affected by the change.